1. Field of the Disclosure
The present disclosure relates to a high-speed digital-to-analog converter and more specifically to a latch for synchronizing control signals for switching switches that steer current to the output of the digital-to-analog converter.
2. Description of the Related Art
High-speed and high-accuracy digital-to-analog converters (DACs) are important building blocks for many signal processing and telecommunication systems. A DAC is a device that converters a digital signal into an analog signal in the form of, for example, current, voltage or electric charge. Due to the ever increasing digital processing power and speed of modern chips, the need for DACs with higher sampling speed is on the rise. For example, 3D high-definition televisions (HDTVs) use DACs with 200 Mega samples per second (MSPS) while telecommunication transmitters use DACs with over 300 MSPS. In addition to the high sampling speed, many of these applications also require very high linearity and high Spurious-Free Dynamic Range (SFDR) in the output analog signal.
Generally DACs use multiple switches to steer current to an output. The switches are operated by digital signals generated by a chain of digital signal processing. As the switches are turned on or off by the digital signals, jitter in the digital signals to the switches may degrade linearity performance and add spurious noises at the analog output. With high-speed DACs, the situation is especially critical since jitter at the digital signals tends to cause more pronounced effect as the frequency increases.
Another important factor in high-speed DACs is data dependent switching of switches. Data dependent switching can be caused partly due to the asymmetry in the beginning transition and ending transition of “on” pulse (e.g., “1” pulse) and “off” pulse (e.g., “0” pulse). Generally, the transition time for turning on the pulse and turning off the pulse are asymmetric. Due to such differences in transition time, data stream including combinations of “on” pulses and “off” pulses generate noise in the analog output of the DACs that is dependent on digital signals provided to the DACs. Although differential switching can partly remove nonlinearities, some data-dependent noise remains even when differential switching is used.